The invention relates to a stack height determination mechanism for a stack consisting of flat material, preferably sheet paper, with at least one sensor to determine stack height and such a stack height control mechanism with such a stack height determination mechanism.
A stack height determination mechanism is disclosed in U.S. Pat. No. 6,318,954, issued Nov. 20, 2001, in the name of Claassen et al., which proposes providing on the edge of the stack a row of sensors disposed above each other which determine stack height by recording to the extent to which light emitted from the stack is reflected or not. The disadvantage of this configuration exists in the fact that a material, paper in particular, which does not lie neatly or is wrinkled, will result in a malfunction indication. In addition, a crease or bulge in the measurement range is recorded as stack height, even if it does not exist in other areas or is still deposited after measurement. A stack cannot be exactly positioned in this manner, which is particularly disadvantageous if further material is to be delivered and the plane of conveyance is incorrect as a result of the inexact setting.
The object of the invention therefore is to construct a stack height determination mechanism in such a way that exact stack height determination is possible, especially in order to exactly position the stack for the next delivery of material.
The object is solved in accordance with the invention in that a flat element to determine the height of the stack is brought into a bearing position on the stack and that this bearing position is determined by at least one sensor.
The advantage of the invention consists in the fact that the height of the stack is exactly determined, independently of whether there are wrinkles or bulges in the material at the measurement location. At the same time, the height determined corresponds to the height of the delivered material occupied by the latter after complete delivery on the entire surface. Stack height determined in this manner provides a substantially more exact measurement, in particular for a height setting which is used to set the function-adjusted plane of conveyance for additional material to be delivered.
The height of the flat element, which represents a measurement for the height of the stack, can be determined in different ways. Approximation sensors, ultrasonic sensors, stop switches or other sensors are possible. As an advantageous refinement it is proposed that at least one sensor is an optical sensor. Moreover, it can be a single sensor whose function will be elucidated later, or it is possible to dispose a row of optical sensors in such a way that several height positions of the flat element can be determined by such row of optical sensors.
The flat element can be an element provided for this measurement purpose which is equipped with a drive mechanism and control device which moves the element into the measurement position and again removes same from the latter for delivery of additional material. As an expedient development, however, it is proposed that the flat element is a functional element of a delivery device for the flat material. This has the advantage that the separate provision of a flat element and its drive and control device can be dispensed with and, as a result, stack height determination substantially simplified. An expedient refinement provides that the flat element is the holding-down clamp of a delivery device. Because such holding-down clamp functions to position delivered material on the stack, exact height determination by it is assured. In particular, it determines stack height on the side at which additional material is being fed and, consequently, also determines the height which is controlling for the setting of the plane of conveyance.
One refinement for the disposition of a sensor on a holding-down clamp provides that at the back end of the stack the delivery device exhibit horizontally and vertically movable tongues, actuatable and horizontally movable rollers, and at least one horizontally and vertically movable holding-down clamp, in which case drive mechanisms and a control device so constructed are provided, that a flat material, lying between the rollers and tongues, is conveyed by the rollers into its delivery position, that the holding-down clamp then presses the flat material onto the stack, that this height position of the holding-down clamp is determined by at least one sensor and that subsequently the rollers are lifted and the tongues withdrawn from the stack counter to the direction of conveyance and that to convey additional material the holding-down clamp is lifted, withdrawn from the delivery area and that the tongues and rollers are again conveyed into the position for the delivery of additional material. In this manner, after every delivery of a material, stack height is determined and can, therefore, always be exactly set.
The invention further relates to a stack height control mechanism with a stack height determination device. According to a stack height control mechanism, a stack height adjustment device and a control mechanism are provided where stack height is determined after every delivery of material and by the control mechanism causes the stack height adjustment device to set the target height. A stack height control mechanism can be equipped with a stack height determination mechanism of all the aforementioned specific embodiments. The stack height adjustment control mechanism is, however, preferably constructed in such a way that after the flat element bears on the stack, the stack height adjustment device depresses the stack until a sensor responds, which sensor is disposed in such a manner that it determines target stack height attainment through the corresponding position of the holding-down clamp.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.